Ladybird: Detect changes to the default audio device

When the default audio device changes on the host, it's convenient to
automatically switch to that device rather than needing to reload the
page to update.

Ladybird/AudioCodecPluginLadybird.cpp

@@ -27,6 +27,7 @@ struct AudioTask {
         Pause,
         Seek,
         Volume,
+        RecreateAudioDevice,
     };
 
     Type type;
@@ -82,20 +83,64 @@ private:
         No,
     };
 
-    void run() override
+    struct AudioDevice {
+        static AudioDevice create()
         {
-        auto devices = make<QMediaDevices>();
+            auto const& device_info = QMediaDevices::defaultAudioOutput();
-        auto const& device_info = devices->defaultAudioOutput();
 
             auto format = device_info.preferredFormat();
             format.setChannelCount(2);
 
             auto audio_output = make<QAudioSink>(device_info, format);
-        auto* io_device = audio_output->start();
+            return AudioDevice { move(audio_output) };
+        }
+
+        AudioDevice(AudioDevice&&) = default;
+
+        AudioDevice& operator=(AudioDevice&& device)
+        {
+            if (audio_output) {
+                audio_output->stop();
+                io_device = nullptr;
+            }
+
+            swap(audio_output, device.audio_output);
+            swap(io_device, device.io_device);
+            return *this;
+        }
+
+        ~AudioDevice()
+        {
+            if (audio_output)
+                audio_output->stop();
+        }
+
+        OwnPtr<QAudioSink> audio_output;
+        QIODevice* io_device { nullptr };
+
+    private:
+        explicit AudioDevice(NonnullOwnPtr<QAudioSink> output)
+            : audio_output(move(output))
+        {
+            io_device = audio_output->start();
+        }
+    };
+
+    void run() override
+    {
+        auto devices = make<QMediaDevices>();
+        auto audio_device = AudioDevice::create();
+
+        connect(devices, &QMediaDevices::audioOutputsChanged, this, [this]() {
+            queue_task({ AudioTask::Type::RecreateAudioDevice }).release_value_but_fixme_should_propagate_errors();
+        });
 
         auto paused = Paused::Yes;
 
         while (true) {
+            auto& audio_output = audio_device.audio_output;
+            auto* io_device = audio_device.io_device;
+
             if (auto result = m_task_queue.dequeue(); result.is_error()) {
                 VERIFY(result.error() == AudioTaskQueue::QueueStatus::Empty);
             } else {
@@ -136,6 +181,10 @@ private:
                     VERIFY(task.data.has_value());
                     audio_output->setVolume(*task.data);
                     break;
+
+                case AudioTask::Type::RecreateAudioDevice:
+                    audio_device = AudioDevice::create();
+                    continue;
                 }
             }